In order to determine their velocity and the distance covered on the track, railway vehicles are equipped with wheel sensors, allowing measurement of the rotation of one or several wheels of the vehicle.
The measurements conducted from wheel sensors are often unusable and inaccurate, because of the sliding of the wheel relatively to the rail. This sliding either occurs during acceleration phases of the vehicle or during braking phases.
Conducting measurements of acceleration, velocity and position from an inertial unit was contemplated, but the information provided by the inertial units fitting out the vehicles is also marred with errors which result from inaccuracies or biases related to the technology used.
In practice, in order to reduce the manufacturing costs, these inertial units commonly apply MEMS technologies which delivered by design of values having a bias.